1. Field of the Invention
This invention relates to a vehicle obstacle detecting system having an obstacle detector (such as a laser radar) mounted on a vehicle, more particularly to an obstacle detecting system which can determine whether the obstacle detector is mounted appropriately in position on the vehicle.
2. Description of the Related Art
Various obstacle avoidance techniques have hitherto been proposed. For example, Japanese Laid-open Patent Application Hei 6(1994)-298022 teaches detecting the distance to an obstacle (e.g., another vehicle running ahead on the road) and automatically operating a brake, if needed, so as to avoid the contact with the obstacle.
In this prior art technique, the acceleration of the another vehicle (obstacle) is detected and, based on the detected acceleration, a first threshold value (distance) for avoiding the obstacle by braking is determined. At the same time, a second threshold value (distance) for avoiding the obstacle by steering is determined based on the assumption that the subject vehicle passes after time .tau., measured from a certain point with a lateral acceleration bo. Using a sensor such as a laser radar, the distance to the obstacle is detected and if the detected distance falls below the first and second threshold values, the brake is automatically operated.
In this kind of obstacle avoidance control, all possible obstacles or objects on the road on which the vehicle is traveling, should accurately be detected without fail using a sensor such as radar. However, there exist many objects on a road such as bridges, road signs, etc. They are present well above the road surface and are free from contact with the vehicle. Moreover, there are other objects on the road surface such as cats-eyes (reflectors) provided at the lane markings which are also not dangerous to the vehicle.
For that reason, when a radar is used, the radar should preferably be mounted on the vehicle in such a manner that the range for scanning, in particular that in the gravitational (vertical) direction, is set to be narrow so that the radar beam emits only in the horizontal direction parallel with the road surface.
However, the radar, once thus mounted on the vehicle, may occasionally be out of the position due to, for example, a slight collision with other vehicle or object, causing the radar beam to incline upward or downward. Even when the radar is kept in position, the vehicle pitch angle may deviate from the initial angle due to trouble in the suspension, use of tires other than those recommended, or overloading, causing the radar beam to incline in the gravitational direction.
When this happens, the radar is less likely to detect an obstacle on the road with accuracy and hence, it becomes sometimes difficult to effectively conduct a desired obstacle avoidance control.